1. Field of the Invention
The present invention relates to a method for planning orthognathic surgery, especially relates to a 3D planning and prediction method for optimizing facial skeleton symmetry in orthognathic surgery.
2. Description of the Related Art
Orthognathic surgery is commonly practiced in oral and maxillofacial region. Such surgery is performed to correct positions of jawbones with asymmetric facial structure, severe skeletal discrepancy or orthodontic problems. Before performing an orthognathic surgery, a surgeon first diagnoses oral and maxillofacial problems of the patient, then makes a pre-surgical plan with 2-D cephalometric analysis and performs the orthognathic surgery accordingly. Based on the pre-surgical plan, jawbones of the patient may be segment and re-aligned in a predetermined position. If the pre-surgical plan is not carefully made, the surgery may not have a predicted treatment effect on the patient.
When making a pre-surgical plan for an orthognathic surgery, cephalometric x-ray images of the patient's head in front and lateral directions will be taken by a surgeon to determine a two-dimensional post-surgical target position of jawbones by using transparent tracing paper with feature lines of jawbone edges. A plaster dental cast including upper and lower jaws will be made according to the patient's oral cavity. The plaster dental cast is provided for the surgeon to simulate the orthognathic surgery according to the target position of jawbones to show a possible post-surgical appearance of jaws before putting the surgery into practice. However, because of the lack of three-dimensional information, such as rotation angles of jaws, post-surgical relation between the positions of upper and lower jaws cannot be precisely predicted by the cephalometric x-ray photos and the surgeon's experiences. Therefore the orthognathic surgery may lead to a result that dental occlusion is correct but facial appearance is still asymmetric.
In conclusion, a pre-surgical plan made by foregoing traditional method has disadvantages as follows:
1. Positions of teeth and jaws cannot be simultaneously considered, the post-surgical result often leads to perfect dental occlusion with asymmetric jaws.
2. Try-and-error adjustment of two-dimensional cephalometry transferred to the dental cast is time-consuming and is difficult to satisfy both occlusion function and facial aesthetic.
3. Two-dimensional cephalometry combined with substantial plaster dental cast cannot provide rotation angles of jaws in three-dimensional space.
4. Taking rest occlusion as a prior consideration to x-ray cephalometry is difficult to achieve substantial facial skeleton symmetry.
To overcome the shortcomings, the present invention provides a 3D planning and prediction method for optimizing facial skeleton symmetry in orthognathic surgery to mitigate or obviate the aforementioned problems.